Multicellularity
•
Colonies: cyanobacteria and
choanoflagellates
•
Sponges as organisms
Cyanobacteria - among the
oldest fossils
Stromatolite section
Stromatolites: colonies of cyanobacteria
Figure 26.3x2 Filamentous cyanobacteria from the Bitter Springs Chert
Figure 26.2 Clock analogy for some key events in evolutionary history
Figure 27.11 The cyanobacterium Anabaena and its nitrogen-fixing heterocysts
Development and communication in Anabaena
Crucial components need to be identified to
understand the process of heterocyst cellular
differentiation. What is the switch that commits a cell
to differentiate? How is transcription controlled at
different stages of development? Is there a single
master transcriptional regulatory control or do
several regulators work in parallel? What
mechanisms are involved in expression of the
nitrogen-fixation genes?
Figure 26.1 Some major episodes in the history of life
Figure 32.8 Animal phylogeny based on sequencing of SSU-rRNA
colonial choanoflagellate
Enzymes typical of true animals (metazoans) are found in
their colonial protist anscestors, e.g. tyrosine kinase is found
in choanoflagellates.
tyrosine
Multicellularity
•
Colonies: cyanobacteria and
choanoflagellates
•
Sponges as organisms
Figure 33.2 Sponges
Figure 33.3 Anatomy of a sponge
It’s what’s between cells that defines
multicellularity in animals.
Integrins are cell-surface proteins that sense the extracellular
protein (matrix) environment and signal to the cell to control
differentiation, survival and migration of cells.
Figure 26.2 Clock analogy for some key events in evolutionary history
Multicellularity
•
Colonies: cyanobacteria and
choanoflagellates
•
Sponges as organisms